1. Technical Field
The present invention relates to a radial-ply tire having a belt consisting of 4 or more plies and disposed on a carcass with interposed rubber pads, and more particularly to a radial-ply tire improved in camber thrust characteristic.
2. Background Art
FIG. 3 is a schematic partial section view showing a conventional radial-ply truck/bus tire which is generally used at an inflation pressure not less than 4 kg/cm.sup.2.
The circumferential surface of a carcass 10 is braced by a belt 20. This belt 20 consists of four plies 21, 22, 23 and 24. These belt plies may for example be rubber pads steel cords, with pad rubber 30 being interposed between the ends of these plies and the carcass 10. Of the four plies, the second ply 22 has the maximum width NBW, with the third and fourth plies 23, 24 having progressively diminishing widths. Furthermore, tread rubber 40 is laid on the belt 20. The width of this tread rubber 40, which means the tread width TW, is larger than the maximum belt width MBW.
In the conventional radial-ply tire described above, in which the widths of all the belt plies 21, 22, 23, 24 are smaller than the tread width TW, the tread stiffness shows a sudden decrease at the side edges of the tread rubber 40 so that when the tire has been caught in a rut, a negative camber thrust is generated, provided that the camber in the upward direction along the slope of the rut is taken as being the positive camber. Therefore, the problem arises that unless the steering wheel is turned much, the vehicle cannot be successfully dislodged from the rut.
With the foregoing in view, it is an object of the present invention to achieve a positive camber thrust with a radial-ply tire having a belt of 4 or more plies on a carcass through an interposed rubber pads.